The invention relates generally to methods and systems for printing computer-generated images and more particularly to a method and apparatus for accelerating the process of printing a sheet on a output display device.
A computer system can output data to a wide variety of output display devices. Output display devices such as laser printers, plotters, imagesetters, and other printing devices produce an image or "visual representation" on a sheet of paper, a printing plate or the like. A printing device can print dots on a piece of paper corresponding to the information of a bitmap or pixelmap (where a pixelmap is characterized as having a depth of two or more bits). A "raster" printing device creates a visual representation by printing an array of pixels arranged in rows and columns from the bitmap.
One type of printing device is a printing press. A printing press may be used to produce books, newspapers, pamphlets, posters and other single and multi-page printed matter. The printing press advantageously prints multiple pages of printed matter at the same time onto a single sheet. Other devices used for printing multiple pages at the same time include imagesetters and plate setters.
When printing multiple pages, the individual pages are arranged in one or more sheets. Each sheet includes a layout of pages that may be ordered or otherwise optimized to facilitate post-printing processes. For example, the layout of the sheet may be arranged such that individual pages are in sequence when folding occurs.
Printing devices that produce output in response to page description language input are widely used. A page description language (PDL) is a high level language for describing objects to be displayed by an output device. A printing device may receive page description data in the form of a PDL file. In order to produce a finished sheet, a printing device typically interprets all of the objects contained in the PDL file. Thereafter, the printing device renders objects within the data into bitmaps and prints the sheet. Depending on the printing device, printing of a band may begin as soon as the objects within that band are rendered or printing may not begin until all of the objects for the sheet have been rendered.
Imposition is a process of arranging the pages for a sheet to achieve a proper sequence or position of each page relative to other pages. Imposition is performed to facilitate post-printing processes including fold and cut operations and binding. Conventional imposition processes are executed on a computer workstation prior to the printing process. A conventional imposition process operates on one or more PDL files or image data files and layout information for a given sheet. The PDL files are representative of the various pages (or sub-pages) of content to be displayed on a given sheet. The layout information describes how the pages are to be arranged to achieve the desired output result. The output of an imposition process is generally of the form of a single PDL file that includes all the data required (including external references, if any) for a printing device to print the sheet.